Footnotes

• Contributors All the authors had carefully read the article and analyzed their methods and data. CL and KL suggested comment points and drafted this manuscript. KL critically revised the comment points of this manuscript and is the author responsible for this paper. CL revised comment points and this paper. All authors had seen and approved the final manuscript.

• Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

• Competing interests None declared.

• Provenance and peer review Not commissioned; internally peer reviewed.